It's not that it isn't gaining traction. Rather it's just a massive, herculean undertaking that Sean and co have been working on in the background. Hell Sean only just a few months ago started posting demos on twitter of their C++ borrow checker proof of concept finally working in moderately non-trivial examples.

This isn't to say that their progress isn't going well. Rather they've been making incredible progress at a rate nobody really thought possible but this is just a truly Herculean effort.

Also this proposal is literally only 2 days old. The work has been in progress for years but this is to my knowledge the first time it has actually been proposed formally.

Do you see this realistically getting implemented?

Because C++ is big and old and everyone wants it to be something different. Functional programmers want it to be more functional, OOP developers want more object oriented, etc. And the syntax must look familiar. And everything must be backwards-compatible and all older legacy code needs to work fine. And it must have next-to-no runtime cost. Etc.

Making any changes to C++ is a slow process - as it is for any older and larger language.

Plus...I think memory safety is a pretty low priority area for C++, frankly. It's harder to shoehorn in at this point, C++ has never prioritized it over raw performance or flexibility.

There's no point. Rust can already be added incrementally in an existing C++ or C project. Like how Servo was in Firefox, or Rust in the Linux kernel.

If it would work, it would gain traction. Guaranteed.

C++ is a very slow moving language. There are various rumblings about making it memory safe, but if we get a proper memory safe C++ it'll probably be in the '30s.

It just looks like an ugly version of rust.